If you jump up as
hard as you can, gravity pulls you back down to the earth. If you were
standing on another planet and jumped up, you might be able to jump
higher, or maybe not as high.

How strong the pull feels depends on how big the planet is. On planets
with more mass than earth, you would feel heavier, and on planets with
less mass you'd feel lighter. (Mass just means the amount of
"stuff" the planet is made of.